Systems and methods for counting people provide valuable statistical information for a wide range of applications. For example, one application is the need to determine the total number of customers passing through an entrance into a shop. Another application is the need to determine the net number of passengers on a mass transportation vehicle at each point along its route.
Systems adapted for such applications are described in U.S. Pat. Nos. 4,000,400, 4,303,851, SU 1336061, SU 1418780, SU 1441427 and NL 9100591. However, such systems suffer from the drawback that they are incapable of providing accurate information under the working environments in which they are required to operate, for example, confined conditions, the possibility that a person who starts passing through an entrance may turn back, entrances which enable two or more people to pass therethrough simultaneously, and the like.
In particular, U.S. Pat. No. 4,122,331 (Tsubota et al.) describes a device for counting the number of people entering or exiting a given area, including a mat switch having a plurality of normally open independent switches arranged in the form of a ladder and a plurality of resistors each connected to one of the plurality of switches. The switches and the resistors are so configured that the output resistance of the mat switch undergoes a monotonic reduction as switches are successively closed by the pressure of a person's foot as he moves in a predetermined direction along the mat switch. Thus, the change in the output resistance of the mat switch provides an indication as to the person's progress along the mat switch and thus permits the number of people entering or leaving the area to be counted.
In other words, the principle upon which Tsubota et al.'s device is based is that a person's progress along the mat switch can be monitored by an analysis of the change in the resistance of the mat switch as a consequence of a person walking along the mat switch in such a manner that both of the person's feet make consecutive contact with the mat switch. However, there are many environments, particularly in confined areas, in which a landing stage is insufficiently long so as to accommodate a full stride of a person. But, if the mat switch disclosed by Tsubota et al. were to be shortened so as to accommodate less than a full stride, the mat switch would merely provide a one-off instantaneous recording of a person's presence thereon and would not allow determination of whether the person completely passed through the entry point.
It is an object of the invention to provide systems and methods having advantages in the above respects.